New insights on scrape-off layer plasma turbulence

​Seminar by Paolo Ricci, Swiss Plasma Center, EPFL.

Abstract

One of the greatest uncertainties in the success of ITER and future fusion reactors is related to
the turbulent dynamics of the plasma fusion fuel in the scrape-off layer (SOL). The plasma
behavior in this region governs the overall confinement properties of the device, regulates the
impurity dynamics and the level of fusion ashes, and determines the heat load to the tokamak
vessel walls – a showstopper for the whole fusion program if material requirements cannot be met.
A project is being carried out in Lausanne focused on deepening our understanding of plasma
turbulence in the SOL and the Global Braginskii Solver (GBS) code has been developed for this
purpose. By solving the drift-reduced Braginskii equations coupled to a kinetic equation for the
neutrals, the code evolves self-consistently the SOL plasma dynamics as it results from neutral
recycling, turbulent transport, and plasma losses at the vessel. These simulations have allowed
us to advance the basic understanding of SOL turbulence, making progress in the identification of
the driving instabilities and in estimating the turbulence saturation amplitude, the SOL pressure
scale length, and the generation of intrinsic toroidal rotation. The comparison of our
theoretical and simulation results against data from several tokamaks worldwide yielded very good
agreement.